This application claims the priority of Korean Patent Application No. 2003-37830, filed on Jun. 12, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a boost converter, and more particularly, to a power supply apparatus which adjusts the output voltage of a boost converter according to an input voltage.
2. Description of the Related Art
In general, in a case of an electro-communication machinery, a computer system and an electronic machinery with a large capacity, a switching mode power supply (SMPS), which converts ordinary input alternating current (AC) power to direct current (DC) power and then converts the AC power to DC power with the same power again using a switching step, is widely used.
FIG. 1 is a block diagram of the construction of a general boost converter power supply apparatus. A boost converter is a type of power supply apparatus that can always make output voltage higher than input voltage, and generates the regularly boosted output voltage from the regulated AC input voltage through a pulse width modulation (PWM) operation.
A regulator 100 shown in FIG. 1 is composed of a bridge diode circuit typically subjected to 90–260 VAC and the regulator 100 converts the input AC voltage into a DC voltage of a ripple waveform. A transformer T induces the predetermined voltage in a secondary coil by inputting the DC voltage from the regulator 100. A regulating diode D and a smoothing condenser C output a predetermined voltage Vout by regulating and smoothing the voltage induced in the secondary coil of the transformer T. A switching unit Q is composed of a switching component such as a field effect transistor (FET), and its on/off time is controlled by a PWM control signal output from a controller 101. Therefore, the switching unit Q switches the operation of the transformer T by the PWM signal output from the controller 101.
The controller 101 senses the voltage Vout output via the regulating diode D and the smoothing condenser C and then outputs a PWM signal, whose duty ratio is adjusted, to the switching unit Q. At this time, the controller 101 senses the input voltage and output voltage, and outputs the fixed PWM signal for generating the output voltage boosted further than the input voltage to the switching unit Q.
The description of the boost converter power supply apparatus is disclosed in U.S. Pat. No. 6,175,218.
The boost converter power supply apparatus is largely classified into a method of fixing the output voltage and a method of linearly changing the output voltage according to the input voltage.
The method of fixing the output voltage generates a fixed output voltage of 375˜400VDC so as to correspond to all AC input voltage in a case where the boost converter is used for power factor correction (PFC) of a general AC input voltage. However, since a high voltage is always generated even when the AC input voltage is very low, a large switching loss occurs in the switching component, and therefore, the efficiency is decreased. Also, since the output voltage is fixed, in a case where an AC input voltage is input over 300V due to an unstable AC input voltage, products using the power of a particular province or a country must be redesigned.
The method of linearly changing the output voltage according to the input voltage solves the switching loss according to the fixed high output voltage. However, since an output voltage according to a low AC input voltage becomes too low, the energy stored in an output condenser C becomes small. Thus, a hold-up time, the time falling from full-charged voltage to minimum operation voltage of the product, becomes short, and a problem of power supply in the products requiring a long hold-up time occurs, especially, in the image products.